Mechanism of photoregulated carotenogenesis in rhodotorula minuta VIII. Effect of mevinolin on photoinduced carotenogenesis

Mevinolin, which is a highly specific competitive inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, was used in a search for photoinducible enzyme(s) other than HMG-CoA reductase in the pathway of carotenoid biosynthesis in Rhodotorula minuta.The photoinduced production of carotenoids was competitively inhibited by mevinolin. The concentration of mevinolin that is required to inhibit completely the production of carotenoids depends on the light dose given to the cells. However, the relationship between the inhibition ratio and the concentration of mevinolin was almost identical regardless of the light dose. These results suggest that the activity of enzymes involved in the formation of HMG-CoA may not be affected by light.When an adequate amount of mevalonate was added to the growth medium that contained sufficient mevinolin for the complete inhibition of the photoinduction of the production of carotenoids, the same quantity of carotenoids was produced as in the absence of mevinolin. Moreover, the production of carotenoids in the presence of both mevinolin and mevalonate was inhibited by cycloheximide.It appears from these results that one or more photoinducible enzymes, such as HMG-CoA reductase, may be present in the carotenogenic pathway beyond mevalonate.